1. Field of Invention
The present invention relates to a vehicular slope determination apparatus and method for determining whether a vehicle is on a slope and to a vehicle height adjust control apparatus using the slope determination apparatus.
2. Description of Related Art
Japanese Patent Application Laid-Open No. SHO 60-92912, for example, describes a technology wherein a slope angle of a road surface (inclination angle of a vehicle body) is detected using a slope angle sensor mounted on the vehicle body and, when the detected upslope angle of the road surface becomes greater, the vehicle height of a rear portion of the vehicle body is increased relative to the vehicle height of a front portion of the vehicle body, so as to eliminate the problem of a reduction of the driver's visual field caused by gravity pulling the driver backward when the vehicle is running on an upslope. Japanese Patent Application Laid-Open No. SHO 60-131308, for example, describes a technology wherein a slope angle sensor is mounted on a vehicle body and, based on the slope angle of the vehicle body detected by the slope angle sensor and vehicle heights detected by vehicle height sensors disposed at individual wheel positions, the vehicle height is controlled so that during travel in a straight line, the vehicle body is maintained horizontally regardless of the inclination angle of the road surface and, during turning at a curve, the vehicle body is inclined in accordance with the centrifugal force. Japanese Patent Application Laid-Open No. SHO 60-131308 also describes an inclination angle sensor wherein a resistor member and an electric conductor member are curved at a predetermined curvature, and arranged in parallel and horizontally, and an electric conductor ball is provided for moving while contacting the resistor member and the electric conductor member at points and, with a predetermined voltage applied to the resistor member, a voltage corresponding to the position of the electric conductor ball is extracted.
However, in the inclination sensor according to the conventional technology described above, it is difficult to always maintain the electric conductor ball stably on the resistor member and the electric conductor member. Therefore, it becomes impossible to always detect the inclination of the vehicle body, that is, the inclination of the road surface, with good stability and precision. Furthermore, this mechanical inclination angle sensor has a complicated construction and requires a high production cost, as in typical mechanical sensors. Furthermore, if vehicle height adjustment is performed when the vehicle is running or stopped on a slope, in particular, a steep slope (for example, a slope at or above an angle of about 30.degree.), a large vehicle height difference between the front and rear portions of the vehicle body results and an appropriate vehicle height adjustment relative to the road surface fails immediately after the vehicle moves from the slope onto a substantially horizontal road, thereby causing problems of interference between the vehicle body and a road surface and the like.